As a conventional tank type vacuum circuit breaker, there is one which is disclosed in, for example, Japanese Unexamined Patent Publication No. 2011-97686; and its simple overview is shown in FIG. 5 and FIG. 6. FIG. 5 is a sectional view showing the conventional tank type vacuum circuit breaker; and FIG. 6 is a relevant part enlarged view showing the conventional tank type vacuum circuit breaker. In the respective drawings, identical or equivalent members and portions will be described with the same reference numerals and letters assigned thereto.
An electrically grounded pressure tank 2 that constitutes a tank type vacuum circuit breaker 1 is installed with a torso portion 2a being kept horizontal and a pair of cylindrical opening portions 2b, 2c are provided on the upper side of the pressure tank 2. Then, the pressure tank 2 includes: cylindrical current transformer mounting portions 2d, 2e, coaxial with the opening portions 2b, 2c and smaller in diameter than the opening portions 2b, 2c; and ring-shaped flange members F provided at connection portions between the opening portions 2b, 2c and the current transformer mounting portions 2d, 2e. Current transformers 7 which are for measuring current are installed on outer peripheral portions of the current transformer mounting portions 2d, 2e. Incidentally, in this example, the opening portions 2b, 2c and the current transformer mounting portions 2d, 2e are connected by welding via the flange members F.
A vacuum valve 4 serving as an electrical device is installed in the pressure tank 2 via a gap formed with respect to the torso portion 2a. The vacuum valve 4 is composed of a tubular vacuum vessel 41 made of insulation material such as ceramics; a fixed conductor 43 which is placed in the vacuum vessel 41, one end of the fixed conductor 43 being joined to an end plate 42 which is for airtight sealing a fixed side end section 41a of the vacuum vessel 41; and a movable conductor 45 which is disposed to be capable of being connected/disconnected to/from the fixed conductor 43, the other end of the movable conductor 45 being extended outside the vacuum vessel 41 via a bellows 44 attached to a movable side end section 41b of the vacuum vessel 41. A fixed contact 43a and a movable contact 45a are formed at a portion where the movable conductor 45 comes into contact with the fixed conductor 43, respectively. Incidentally, the end plate 42, the fixed conductor 43, and the movable conductor 45 are made of conductive material such as copper alloy and aluminum alloy; and the inside of the vacuum valve 4 is airtight held under vacuum.
Opening and closing means 3 by which the fixed contact 43a and the movable contact 45a are connected/disconnected is provided outside the pressure tank. The opening and closing means 3 is made to move the movable conductor 45 in a horizontal direction via an operation rod 5 and an insulation rod 6; and thus, the fixed contact 43a and the movable contact 45a are connected/disconnected to be closed/opened. At this time, the bellows 44 follows the movement of the movable conductor 45; and therefore, the inside of the vacuum valve 8 is held under vacuum.
A fixed side shield 51 and a movable side shield 52 are provided on both sides of the vacuum valve 4. The fixed side shield 51 is disposed so as to cover the fixed side end section 41a of the vacuum valve 4, and is connected to the end plate 42 on the fixed side. The movable side shield 52 is disposed so as to cover the movable side end section 41b of the vacuum valve 4 and an end section of the movable conductor 45, and is connected to a movable side end plate 46 of the vacuum valve 4. The fixed side shield 51 and the movable side shield 52 are made of conductive material such as aluminum alloy and copper alloy; and the surface thereof are each formed by a smooth surface with no edge.
Furthermore, the fixed side shield 51 is fastened to an insulation supporting rod 9 attached to a base plate 8 via an adapter 10; and all constituent components for one phase from the fixed side shield 51 to the operation rod 5 are supported by the insulation supporting rod 9. The insulation supporting rod 9 has strength and size which withstand the weight of the constituent components and a shock during opening and closing operation. Insertion portions 51a, 52a into which one ends of second connection conductors 22a, 32a disposed in center portions of intermediate bushings 210, 310 are inserted are provided at the tops of the fixed side shield 51 and the movable side shield 52. Incidentally, in this example, the insertion portions 51a, 52 have the function of terminal portions of the vacuum valve 4 serving as the electrical device. Furthermore, the opening portions 2b, 2c are provided corresponding to the insertion portions 51a, 52a serving as the terminal portions.
The fixed side shield 51 and the movable side shield 52 are formed so as to cover the fixed side end section 41a and the movable side end section 41b; and thus, electric field concentration at the fixed side end section 41a and the movable side end section 41b of the vacuum valve 4 can be reduced. Furthermore, the supporting configuration by the insulation supporting rod 9 is adopted; and thus, assembly to the base plate 8 and incorporation to the pressure tank 2 can be consolidated. A conductive coil 53 which is for electrically connecting both of the movable conductor 45 and the movable side shield 52 is provided therebetween. The conductive coil 53 made of copper alloy wiring material is formed into a coil spring shape with the whole formed to be circular.
The intermediate bushings 210, 310 in which lower end sections of the second connection conductors 22a, 32a are connected to the insertion portions 51a, 52a at the tops of the fixed side shield 51 and the movable side shield 52 pass through the opening portions 2b, 2c and the current transformer mounting portions 2d, 2e with a distance spaced apart therefrom and are disposed so as to go into lower portions of the porcelain tubes 20. Then, flange-shaped attaching portions 26, 36 integrally formed with insulators 21, 31 are formed in the vicinity of coupling portions of the porcelain tubes 20 and the current transformer mounting portions 2d, 2e on outer peripheral portions of intermediate bushings 210, 310; and the attaching portions 26, 36 are supported and fixed so as to be sandwiched at the coupling portions between the porcelain tubes 20 and the current transformer mounting portions 2d, 2e. 
The intermediate bushings 210, 310 are composed of the hollow-shaped second connection conductor 22a, 32a; insulators 21, 31 which are shown marked with oblique lines in the drawing and are made of thermosetting resin such as epoxy resin coaxially cast-molded around the hollow-shaped second connection conductor 22a, 32a; and ground layers 23, 33 (to be described later) provided on axial central portions of the insulators 21, 31. Protrusion sections 22b, 22c, 32b, 32c whose outer diameters are formed to be large at portions just before being exposed from the insulators 21, 31 are provided in the vicinity of both ends of the second connection conductor 22a, 32a. Then, recess sections 24a, 24b, 34a, 34b formed so that the radial center sides of the insulators 21, 31 are smoothly axially concaved are provided around the periphery of triple junction portions composed of the insulators, the second connection conductors, and insulating gas.
Further, the ground layers 23, 33 made of, for example, conductive rubber or conductive coating material are provided at portions where the outer circumferential surfaces of the insulators 21, 31 are in proximity to grounded members such as the attaching portions of the porcelain tubes 20 and the current transformer mounting portions 2d, 2e, and are in proximity to the second connection conductor 22a, 32a. The ground layers 23, 33 are provided extending to the flange-shaped attaching portions 26, 36 centering on axial central portions of the intermediate bushings 210, 310.
Furthermore, end sections of the insulators 21, 31 on the lower side of the drawing located in the opening portions 2b, 2c of the pressure tank 2 are configured as large diameter portions A thicker in diameter than central portions passing through the current transformer mounting portions 2d, 2e. Similarly, end sections on the upper side of the drawing than the attaching portions of the porcelain tubes 20 are also formed with large diameter portions B thicker in diameter than portions passing through the attaching portions of the porcelain tubes 20 and the central portions.
Ground shields 25, 35 made of, for example, metal such as aluminum or brass, or conductive resin are provided between the large diameter portions A of the insulators 21, 31 and the ground layers 23, 33. The ground shields 25, 35 are placed only on the pressure tank 2 side in FIG. 5, but may be provided on the porcelain tube 20 side.
Furthermore, the large diameter portions A, B are formed at the axial both end sections of the insulators 21, 31, respectively; and thus, space electric fields of the creeping surfaces of the insulators and the circumferences of the insulators can be reduced. Effects by the attachment of the ground shields 25, 35 are similar. The end faces of the porcelain tubes 20 on the sides opposite to the porcelain tube attaching portions (the upper end section side of the drawing) are airtight sealed by terminal conductors 12a, 12b. First connection conductors 11a, 11b whose other ends (the upper side of the drawing) are connected to the terminal conductors 12a, 12b are each formed in a hollow shape and are slidably connected with respect to upper end sections of the drawing of the second connection conductors 22a, 32a by contacts 13a, 13b provided at one ends thereof (the lower side). Through holes 14a to 14d through which the inside of the hollow conductors communicate with the outside thereof are provided in plural numbers in a circumferentially separated manner in the vicinity of end sections on the pressure tank 2 sides of the second connection conductors 22a, 32a and in the vicinity of the terminal conductors 12a, 12b of the first connection conductors 11a, 11b. 
Furthermore, through holes 26a, 36a through which spaces of the current transformer mounting portions 2d, 2e partially communicate with inner spaces of the porcelain tubes 20a are provided at the flange-shaped attaching portions 26, 36 of the intermediate bushings 210, 310. Then, as insulating gas, dry air whose moisture content is less than or equal to 10 ppm is filled inside the pressure tank 2 and the porcelain tubes 20.